Reprint of: Enantiodivergent hydroboration reactions of a racemic allenylsilane with diisopinocampheylborane and Curtin-Hammett controlled double asymmetric crotylboration reactions of (S)-E-α-phenyldimethylsilyl( ddiisopinocampheyl)-crotylborane

Article abstract of DOI:10.1016/j.tet.2013.06.053

The enantiodivergent hydroboration reactions of racemic allenylsilane (±)-4 with (^dIpc)₂BH and subsequent crotylboration of achiral aldehydes with the product crotylborane (S)-E-5 at -78 C provide (E)-δ-silyl-anti-homoallylic alcohols 6 in 71-89% yield and with 93-96% ee. Intriguingly, mismatched double asymmetric crotylboration reactions of enantioenriched chiral aldehydes 20 with (S)-E-5 proceed under Curtin-Hammett control to give anti-β-hydroxylcrotylsilanes 24 as the only products.

Full text of DOI:10.1016/j.tet.2013.06.053

Tetrahedron 69 (2013) 7551e7558
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Reprint of: Enantiodivergent hydroboration reactions of a racemic
allenylsilane with diisopinocampheylborane and CurtineHammett
controlled double asymmetric crotylboration reactions of
(S)-E-
a
-phenyldimethylsilyl(ddiisopinocampheyl)-crotylboraneq
*
Ming Chen, William R. Roush
Department of Chemistry, The Scripps Research Institute, Florida, 130 Scripps Way, Jupiter, FL 33458, USA
a r t i c l e i n f o
a b s t r a c t
The enantiodivergent hydroboration reactions of racemic allenylsilane (ꢀ)-4 with (dIpc)2BH and
subsequent crotylboration of achiral aldehydes with the product crotylborane (S)-E-5 at ꢁ78 ꢂC provide
Article history:
Received 27 February 2013
Received in revised form 20 April 2013
Accepted 22 April 2013
(E)-d-silyl-anti-homoallylic alcohols 6 in 71e89% yield and with 93e96% ee. Intriguingly, mismatched
double asymmetric crotylboration reactions of enantioenriched chiral aldehydes 20 with (S)-E-5 proceed
under CurtineHammett control to give anti- -hydroxylcrotylsilanes 24 as the only products.
Ó 2013 Elsevier Ltd. All rights reserved.
Available online 21 June 2013
b
Keywords:
Enantiodivergent hydroboration
Mismatched double asymmetric
crotylboration
CurtineHammett control
1. Introduction
We envisioned that allene hydroboration reactions with chiral
borane reagents could provide an exceedingly simple means to
The asymmetric crotylation reaction of carbonyl compounds is
one of the most widely utilized methods to synthesize stereo-
chemically defined acyclic molecules.1 However, for many synthetic
applications the terminal vinyl groups embedded in the homo-
allylic alcohol products must be transformed into other functional
groups via several step reaction sequences. Carbonyl crotylation
access chiral, non-racemic a
-functionalized allylborane reagents.3
Several chiral, non-racemic crotylboranes have been developed
recently in our laboratory by using this strategy.4 For example,
as shown in Scheme 1, the enantioselective hydroboration of racemic
allenylstannane (ꢀ)-1 with (ddiisopinocampheyl)borane [(dIpc)2BH]
provides the enantioenriched a-tributylstannyl crotylborane, (S)-E-2.
with
-substituted allylmetal reagents) provide homoallylic alcohols
with a functionalized olefin unit, however the preparation of
a
-functionalized allylmetal reagents (specifically, non-racemic
Subsequent crotylboration reactions of aldehydes with (S)-E-2 give
a
such reagents, in particular enantioenriched
a-substituted cro-
tylmetal reagents, remains largely underdeveloped.2 Therefore,
development of enantioselective methods for the synthesis of
chiral, non-racemic
a-functionalized allylmetal reagents remains
an important objective in methodology development.
DOI of original article: http://dx.doi.org/10.1016/j.tet.2013.04.098.
q
A publisher’s error resulted in this article appearing in the wrong issue. The
article is reprinted here for the reader’s convenience and for the continuity of the
special issue. For citation purposes, please use the original publication details;
Tetrahedron, 69(26), pp. 5468-5475.
* Corresponding author. Tel.: þ1 561 228 2450; fax: þ1 561 228 3052.
E-mail address: roush@scripps.edu (W.R. Roush).
Scheme 1. Enantioconvergent and enantioselective hydroboration of Racemic Alle-
nylstannane (ꢀ)-4) and proposed enantioselective hydroboration of racemic alle-
nylsilane (ꢀ)-4.
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.06.053

7552
M. Chen, W.R. Roush / Tetrahedron 69 (2013) 7551e7558
(E)-
d
-stannyl-anti-homoallylic alcohols 3 in good yields and with
carried out with (dIpc)2BH (1 equiv) in toluene at ꢁ25 ꢂC to ꢁ15 ꢂC
for 8 h, followed by treatment of the resulting crotylborane with
0.45 equiv of aldehyde at ꢁ78 ꢂC, homoallylic alcohols 6aef
(93e96% ee) were obtained in 71e89% yields (based on the alde-
hyde as limiting reagent) from both aromatic and aliphatic alde-
hydes (Scheme 2, bottom panel). Ketone 8 was also formed in these
reactions. The absolute stereochemistry of homoallylic alcohols 6
was assigned by using the modified Mosher ester analysis.8 The
anti-stereochemistry of 6d was verified by protiodesilylation (TBAF,
DMSO, 80 ꢂC) and comparison of the spectroscopic properties of the
derived anti-homoallylic alcohol with an authentic sample.6
In contrast to our previously reported enantioconvergent
hydroboration of allenylstannane (ꢀ)-1,4a the data in Scheme 2 for
the hydroboration of racemic allenylsilane (ꢀ)-4 with (dIpc)2BH
suggest that this reaction proceeds via an enantiodivergent path-
way. As illustrated in Scheme 3 (Panel A), hydroboration of alle-
nylsilane enantiomer (P)-4 with (dIpc)2BH occurs preferentially on
the re-face of the methyl substituted olefin of (P)-4, anti to
PhMe2Sie to give intermediate (R)-Z-9 (first equation of Panel A)
We presume that this reaction is stereochemically matched,4a,9
since the enantioselectivity of this step parallels the enantiose-
lectivity known for the hydroboration of (Z)-olefins with
(dIpc)2BH.4a,9 Subsequent 1,3-shift of the boryl unit of (R)-Z-9 gives
crotylborane (S)-E-5. On the other hand, hydroboration of (P)-4
excellent enantioselectivity.4a The vinylstannane unit in homoallylic
alcohols 3 can be used in a variety of subsequent transformations.5
Importantly, the enantioselective hydroboration of allenylstannane
(ꢀ)-1 proceeds in an enantioconvergent manner, with both enan-
tiomers of the racemic allene (ꢀ)-1d(P)-1 and (M)-1dbeing con-
verted into the same crotylborane intermediate, (S)-E-2. Therefore,
the synthesis of an enantiomerically pure allenylstannane precursor
is not required to access (E)-d-stannyl-anti-homoallylic alcohols 3
with high enantioselectivity and high chemical efficiency.
In our continuing efforts to expand the scope of enantioselective
allene hydroboration reactions for the synthesis of a-functionalized
allylboranes, we envisioned that an analogous enantioconvergent
reaction might be possible using racemic allenylsilane (ꢀ)-4 as the
substrate. If so, the
a-silyl-crotylborane (S)-E-5 that would be
generated would provide access to enantioenriched (E)-d-silyl-anti-
homoallylic alcohols 6 (Scheme 1). The vinylsilane unit of 6 is as
useful for many subsequent transformations as is the vinylstannane
unit of 3. We describe here the results of our studies on the
enantioselective hydroboration of racemic allenylsilane (ꢀ)-4 with
(dIpc)2BH.6
2. Results and discussion
In initial experiments, treatment of racemic allenylsilane (ꢀ)-47
with (dIpc)2BH (1 equiv) in toluene at 0 ꢂC for 4 h, followed by
addition of benzaldehyde (1 equiv) at ꢁ78 ꢂC provided a 5:1 mix-
ture of anti-homoallylic alcohol 6a (76% ee) and the syn isomer 7a
(58% ee) in 41% and 7% yield, respectively (Scheme 2, top panel).
Intriguingly, a ketone by-product 8 (ca. 40%) was also identified.
After extensive evaluation of several reaction parameters,6 we de-
termined that when the hydroboration of racemic allene (ꢀ)-4 was
Scheme 3. Proposed enantiodivergent hydroborationeisomerization pathways for the
two enantiomers of racemic allenylsilane (ꢀ)-4.
Scheme 2. Synthesis of (E)-d-silyl-anti-homoallylic alcohols 6.

M. Chen, W.R. Roush / Tetrahedron 69 (2013) 7551e7558
7553
with opposite regioselectivity on the olefin adjacent to the
PhMe2Sie group (second equation, Panel A) leads to the di-
astereomeric reagent (S)-Z-10, which can isomerize to (R)d-E-5 via
a sequence of reversible 1,3-boratropic shifts. Crotylboration of al-
dehydes with (R)d-E-5 will give the enantiomeric alcohol product,
ent-6. During the optimization of this hydroboration sequence,6 we
observed that the pathway summarized in the second equation in
Panel A of Scheme 3 is suppressed when the hydroboration is
performed at temperatures below ꢁ25 ꢂC. Other pathways for the
hydroboration of allene (P)-4 with (dIpc)2BH, as illustrated in the
third line of Panel A (Scheme 3), are either mismatched with re-
spect to the enantiofacial selectivity of (dIpc)2BH [as determined by
the hydroboration of (Z)-olefins4a,9] or mismatched in that hydro-
boration reaction occurs on the sterically disfavored face of the
allene.
Hydroboration of allene enantiomer (M)-4 with (dIpc)2BH is
stereochemically mismatched when hydrogen adds to the central
allenyl carbon atom.4a,9 The hydroboration transition states pre-
sented in the third line of Panel B (Scheme 3) are mismatched with
respect to the enantioselectivity of (dIpc)2BH (first two transition
structures, third line, Panel B) or because the hydroboration occurs
on the sterically hindered face of allene (M)-4 (third transition
structure, third line, Panel B). The hydroboration pathway pre-
sented in the first line of Panel B (Scheme 3) is also disfavored
(addition to the more hindered face of the allene) and constitutes
a minor pathway leading to crotylborane (S)-E-5 from allene (M)-
4.6 However, the enantioselective hydroboration of (M)-4 can
proceed with boron adding to the central allenyl carbon atom, anti
to the PhMe2Sie group to give vinylborane 11, the precursor to
ketone 8 (as indicated in the second line of Panel B, Scheme 3). The
sense of hydroboration in the conversion of (M)-4 to 11 is consistent
with the enantioselectivity of hydroboration of (Z)-olefins by
(dIpc)2BH,4a,9 and is also favored in that the hydroboration occurs
on the less hindered face of the allene, anti to the distal bulky
PhMe2Sie group. Hence, the hydroboration of (M)-4 to give 11
appears to be stereochemically matched.
The rates of hydroboration of the two enantiomers of racemic
allenylsilane (ꢀ)-4 with (dIpc)2BH are comparable, as indicated by
the fact that the allene recovered from experiments in which
(dIpc)2BH is the limiting reagent (0.45 equiv) is nearly racemic
(<10% ee).6 Therefore, the transformation presented in Scheme 2 is
not a kinetic resolution. Rather, the fact that the enantioselective
hydroboration of the two enantiomers of 4 proceed with different
modes of addition to produce two structurally distinct in-
termediates, (S)-E-5 and 11, respectively, is critical to the success of
this reaction for the synthesis of homoallylic alcohols 6 with high
enantioselectivity.
Scheme 4. Comparison of hydroborationeisomerization pathways for allenylsilanes
12 and (ꢀ)-4.
the hydroboration of (P)-4. Steric repulsion between the methyl
group and the (dIpc)2Be unit in either (R)-Z-9 or (S)-E-15 de-
stabilizes these two species at equilibrium. Subsequent crotylbo-
ration of achiral aldehydes with (S)-E-5 proceeds through the chair-
like transition state TS-1 with pseudo equatorial placement of the
PhMe2Sie group to give (E)-d-silyl-anti-homoallylic alcohols 6
(Scheme 4).
To evaluate the potential of crotylborane (S)-E-5 as a reagent for
organic synthesis, double asymmetric reactions12 with several
representative chiral aldehydes were studied. First, double asym-
metric reactions of
b-alkoxy aldehyde 16 were explored
(Scheme 5). The matched1a,13 double asymmetric reaction of 16 and
reagent (S)-E-5 provided 17 with a 4,6-anti relationship between
the new hydroxyl group and the methoxyl substituent of aldehyde
16, in 71% yield and with >20:1 diastereoselectivity. The mis-
matched double asymmetric reaction of 16 using the enantiomeric
reagent (R)l-E-5 [generated from allene (ꢀ)-4 and (lIpc)2BH] pro-
vided the 4,6-syn diastereomer 18 as the major product of an 8:1
product mixture. Surprisingly, the minor product (19) was de-
termined by 1H NMR analysis to be a crotylsilane regioisomer. As
will be discussed subsequently, crotylsilane adducts, such as 19
derive from crotylboration reactions of (R)l-E-15, which was not
Evidence in support of this analysis, deriving from studies of the
hydroboration of enantiomerically pure allenylsilanes (P)-4 and
(M)-4 with (dIpc)2BH, and 1H NMR studies of the hydroboration
reactions of (P)-4 or (M)-4 with (dIpc)2BH (demonstrating the sig-
nificant production of 11 in the hydroboration of (M)-4) was in-
cluded in our preliminary communication but is not repeated here.6
It is worth noting that, while the resting state of the products of
hydroboration of monosubstituted allenylsilane 12 with (dIpc)2BH
are the (E)- or (Z)-g-silyl-allylboranes,14E or 14Z (depending on the
temperature of the hydroboration reaction),10 the product resting
state for the hydroboration of the 3-methyl substituted allenylsi-
lane 4 with (dIpc)2BH is (E)- -silyl-crotylborane (S)-E-5. Indeed, 1H
a
NMR studies of the hydroboration reaction of (P)-4 with (dIpc)2BH
shows that (S)-E-5 is produced cleanly. Other crotylborane species,
such as (R)-Z-9 or (S)-E-15 are not observed (Scheme 4). Pre-
sumably a combination of the hyperconjugative effect between the
PhMe2Sie group and the adjacent boron atom (analogous to a silyl-
stabilized
being the only observed (and most stable) crotylborane product of
b
-carbocation)11 and steric effects account for (S)-E-5
Scheme 5. Double asymmetric reactions of
E-5 and (R)l-E-5.
b-methoxylaldehyde 16 with reagents (S)-

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M. Chen, W.R. Roush / Tetrahedron 69 (2013) 7551e7558
detected in our NMR analysis of hydroboration reaction mixtures
(vide supra).
The formation of crotylsilane products, such as 19 became much
more prominent in studies of double asymmetric reactions of
a
-methyl branched chiral aldehydes, of interest as precursors to the
di- and tri-propionate fragments found in many polyketide natural
products.14 For example, the matched double asymmetric reaction
of aldehyde 20a with reagent (R)l-E-5 provided a 1:1 mixture of the
expected crotylation product 21 and the crotylsilane regioisomer
22 (Scheme 6).
Scheme 6. Matched double asymmetric reaction of chiral aldehyde 20a with (R)l-E-5.
Scheme 8. Base and acid mediated Peterson elimination reactions of
tylsilanes 24.
b-hydroxy-cro-
Strikingly, crotylsilane adducts 24 proved to be the exclusive
products of the mismatched double asymmetric reactions pre-
sented in Scheme 7. The originally targeted anti,anti-stereotriads
2314 were not detected in any of these experiments. The absolute
stereochemistry of the secondary hydroxyl groups of homoallylic
alcohols 22 and 24 was assigned by using the modified Mosher
ester analysis.8 The olefin geometry of crotylsilanes 22 and 24 was Z
(JZ¼10.8 Hz). The relative stereochemistry of the newly generated
0 ꢂC provided the syn-elimination product 25a. Similar results were
obtained with 24b and 24c (Scheme 8). The coupling constant
between the two vinyl protons of the newly formed olefin in (Z,Z)-
diene 25 is 10.8e11.2 Hz, which is consistent with a (Z)-olefin. On
the other hand, treatment of
b-hydroxyl-crotylsilane 24a with
BF3$OEt2 at ꢁ78 ꢂC provided anti-elimination product (E,Z)-diene
26a. Dienes 26b and 26c were obtained under similar elimination
reactions from 24b and 24c, respectively (Scheme 8). The coupling
constant of the two vinyl protons in the newly formed olefin is
15.2 Hz, which is consistent with an (E)-olefin. Based on these data,
the products obtained from the mismatched double asymmetric
stereocenters in b-hydroxyl-crotylsilanes 24 was assigned by using
both base and acid mediated Peterson elimination reactions.15 As
shown in Scheme 8, addition of 24a to a THF solution of KOt-Bu at
crotylboration reactions of aldehydes 20 with (S)-E-5 are (Z)-anti-
b-
hydroxyl-crotylsilanes 24.
We focus on the attempted mismatched double asymmetric
reactions of Scheme 7 in the following discussion. Assuming that
these mismatched crotylboration reactions proceed through
a chair-like transition state,1 the surprising results in Scheme 7
indicate that the dominant reactive crotylborane intermediate in-
volved in these mismatched double asymmetric crotylborations is
(S)-E-15, with the PhMe2Sie group positioned distal to the boron
atom (Scheme 4) (An analogous reagent must also be involved in
the chemistry summarized in Schemes 5b and 6, but to a lesser
extent as compounds 19 and 22 are not the dominant products of
those reactions). Although it is expected that (S)-E-5 can equilibrate
with (S)-E-15 via a reversible 1,3-boratropic shift.16 1H NMR studies
on the hydroboration of single enantiomer allenylsilanes (P)-4 and
(M)-4 indicate that the amount of (S)-E-15 in the equilibrium
mixture is negligible (not observed). Hence, these data suggest
that: (1) the rate of the mismatched double asymmetric crotylbo-
ration of aldehydes 20aec with (S)-E-15 (Scheme 7) is much faster
than the rate of crotylboration with (S)-E-5; and (2) the rate of
equilibration between (S)-E-5 and (S)-E-15 is much faster than the
rates of the mismatched double asymmetric crotylboration of al-
dehydes 20 with these crotylboranes. Therefore, these reactions
proceed under CurtineHammett control17 with (S)-E-5 funneling to
the more reactive intermediate (S)-E-15 (with respect to aldehydes
Scheme 7. Mismatched double asymmetric crotylboration reactions of chiral alde-
hydes 20 with (S)-E-5. These reactions were performed by treating (ꢀ)-4 with
(dIpc)2BH (1 equiv) in toluene at ꢁ25 ꢂC and warming to ꢁ15 ꢂC over 8 h followed by
the addition of aldehydes 20 (0.4 equiv) at ꢁ78 ꢂC. The mixture was then allowed to
warm to room temperature and stirred for 12 h. The reactions were subjected to
a standard workup (NaHCO3, H2O2) at 0 ꢂC prior to product isolation.
20aec) to give the (Z)-anti-b-hydroxyl-crotylsilanes 24. Although,
CurtineHammett controlled transformations are well documented
in the literature,17 to the best of our knowledge this behavior
has not previously been observed in reactions of allylboration
reagents.

M. Chen, W.R. Roush / Tetrahedron 69 (2013) 7551e7558
7555
Further analysis of this CurtineHammett controlled mis-
matched double asymmetric crotylboration is presented in
Scheme 9. There are four possible transition states for the cro-
tylborations of enantioenriched aldehydes 20aec with crotylbor-
ane species (S)-E-5 and (S)-E-15, TS-2 to TS-5. Among these, TS-2
and TS-3, which lead to formation of 27 and 28, respectively,
operate under FelkineAnh control.18 However, the arrangement of
the crotyl group in TS-2 and TS-3 is mismatched with respect to the
enantiofacial selectivity of the (dIpc)2Bꢁ group.13 Owing to the
unfavorable non-bonding steric interactions in the transition states
(shown in red), TS-2 and TS-3 are likely disfavored. Hence, the rates
of crotylboration via these two transition states are comparatively
slow. On the other hand, TS-4 and TS-5, which lead to the formation
of 23 and 24, respectively, incorporate the proper sense of asym-
metric induction deriving from the (dIpc)2Be units of reagents (S)-
E-5 and (S)-E-15.13 However, the conformation of the aldehyde
position, adjacent to the bulky (dIpc)2Be group in TS-4. Therefore,
crotylborane (S)-E-5 funnels to the more reactive intermediate (S)-
E-15 via a reversible 1,3-boratropic shift under the reaction con-
ditions and the mismatched double asymmetric crotylboration
reactions of aldehydes 20 proceed under CurtineHammett control
via transition state TS-5 with pseudo axial placement of the methyl
group to give (Z)-anti-b-hydroxyl-crotylsilanes 24.
3. Conclusion
We have developed an enantioselective synthesis of (E)-
d-silyl-
anti-homoallylic alcohols via an enantiodivergent hydro-
6
borationecrotylboration reaction sequence that originates with
the enantioselective hydroboration of allenylsilane (ꢀ)-4 with
(dIpc)2BH. Under optimized conditions, homoallylic alcohols 6 were
obtained in 71e89% yield and with excellent enantioselectivity
from racemic allenylsilane (ꢀ)-4 and achiral aldehydes. The prep-
aration of an enantiomerically pure allenylsilane is not required to
produce highly enantioenriched homoallylic alcohol products 6. In
addition, the silyl substituted olefin unit embedded in the homo-
allylic alcohol products is suitable for use in a variety of subsequent
transformations.19e21 A CurtineHammett controlled mismatched
double asymmetric crotylboration of chiral aldehydes 20aec was
discovered, in which reagent (S)-E-5 isomerizes to the less stable,
but more reactive transient reagent (S)-E-15. Specifically, the
transient reagent (S)-E-15, deriving from (S)-E-5 via a reversible
1,3-boratropic shift, reacts with aldehydes 20 faster than (S)-E-5
a
-stereocenter in TS-4 and TS-5 is opposite to what is predicted by
the FelkineAnh model and gauche-pentane interactions18 between
the methyl or PhMe2Si group of the crotyl units and the R group of
the aldehydes could occur in these two transition states (indicated
in blue). Considering the relatively longer SieC bond (estimated to
be 1.85 A) compared to a CeC bond (1.54 A),10 the steric repulsion in
TS-5 is attenuated compared to TS-4, which likely renders TS-5
[crotylboration of 20 with (S)-E-15] to be the most favored transi-
tion state for the mismatched double asymmetric crotylboration of
aldehyde 20. Moreover, the PhMe2Si group is in a more hindered
ꢀ
ꢀ
and provides (Z)-anti-b-hydroxyl-crotylsilanes 24 as the products
instead of the expected vinylsilanes 23. Synthetic applications of
this methodology will be reported in due course.
4. Experimental
4.1. General experimental details
All reaction solvents were purified before use. Tetrahydrofuran,
dichloromethane, diethyl ether, and toluene were purified by
passing through a solvent column composed of activated A-1 alu-
mina. Unless indicated otherwise, all reactions were conducted
under an atmosphere of argon using flame-dried or oven-dried
(140 ꢂC) glassware. The term ‘concentrated under reduced pres-
sure’ refers to the removal of solvents and other volatile materials
using a rotary evaporator with the water bath temperature below
40 ꢂC, followed by removal of residual solvent at high vacuum
(<0.2 mbar). Enantiomeric excesses were determined by the
Mosher method.8
Proton nuclear magnetic resonance (1H NMR) spectra were
recorded on a commercial instrument at 400 MHz. Carbon-13 nu-
clear magnetic resonance (13C NMR) spectra were recorded at
100 MHz. The proton signal for residual non-deuterated solvent (
d
7.26 for CHCl3) was used as an internal reference for 1H NMR
spectra. For 13C NMR spectra, chemical shifts are reported relative
to the
d 77.36 resonance of CHCl3. Coupling constants are reported
in Hertz. Infrared (IR) spectra were recorded as films on a com-
mercial FTIR instrument. Optical rotations were measured using
a quartz cell with 1 mL capacity and a 10 cm path length. Melting
points were determined on a hot stage melting point apparatus and
are uncorrected. High resolution mass spectra were recorded on
a commercial high resolution mass spectrometer.
Analytical thin layer chromatography (TLC) was performed on
Kieselgel 60 F254 glass plates precoated with a 0.25 mm thickness of
silica gel. The TLC plates were visualized with UV light and/or by
staining with Hanessian solution (ceric sulfate and ammonium mo-
lybdate in aqueous sulfuric acid) or KMnO4. Column chromatography
was generally performed using Kieselgel 60 (230e400 mesh) silica
Scheme 9. Transition state analyses of mismatched double asymmetric crotylboration
of aldehydes 20 with crotylboranes (S)-E-5 and (S)-E-15.

7556
M. Chen, W.R. Roush / Tetrahedron 69 (2013) 7551e7558
gel, typically using a 50e100:1 weight ratio of silica gel to crude
d
150.8, 139.3, 134.1, 130.1, 129.3, 128.1, 79.0, 44.0, 40.8, 30.4, 27.3,
product.
26.88, 26.86, 26.5, 17.2, ꢁ2.1, ꢁ2.2; IR (neat) 3435, 3068, 2924, 2852,
1613, 1449, 1427, 1247, 1113, 1067, 999, 844, 827, 730, 699 cmCꢁ1
;
4.2. (1S,2S,E)-4-(Dimethyl(phenyl)silyl)-2-methyl-1-
phenylbut-3-en-1-ol (6a)
HRMS (ESI) m/z for C19H30OSiNa [MþNa]þ calcd 325.1964, found
325.1971.
Crystalline (dIpc)2BH (143 mg, 0.50 mmol) was weighed into
a round bottom flask containing a stir bar in a glove box. (Note: The
crystalline borane should be crushed and pulverized to fine powder
with a glass rod in order to ensure efficient hydroboration). The
flask was capped with a rubber septum and removed from the
glove box. And then the flask was placed in a cold bath (ꢁ25 ꢂC).
Toluene (2 mL) was added slowly to the flask and the mixture
(suspension) was cooled to ꢁ25 ꢂC (w10 min). Racemic allenylsi-
lane (ꢀ)-42 (94 mg, 0.5 mmol) was added neat via a microliter
syringe. This mixture was stirred for 4 h at ꢁ25 ꢂC, and slowly
warmed to ꢁ15 ꢂC for 4 h, during, which time the solid (dIpc)2BH
dissolved to leave a colorless solution. The reaction mixture was
cooled to ꢁ78 ꢂC and freshly distilled benzaldehyde (24 mg,
0.225 mmol) was added at ꢁ78 ꢂC dropwise to the reaction mixture
via microliter syringe. The mixture was stirred for 12 h at ꢁ78 ꢂC.
MeOH (0.1 mL) was added to the ꢁ78 ꢂC solution and the reaction
was allowed to warm to 0 ꢂC. To the 0 ꢂC mixture was added sat-
urated NaHCO3 (0.5 mL) followed by slow addition of 30% H2O2
(1.0 mL). The reaction was stirred vigorously for 5 h at room tem-
perature. Brine (2 mL) was added, the organic layer was separated
and the aqueous layer was extracted with Et2O (3ꢃ3 mL). The
combined organic extracts were dried over anhydrous magnesium
sulfate, filtered, and concentrated under reduced pressure. Purifi-
cation of the crude product was performed by flash column chro-
matography (gradient elution: hexane:Et2O¼200:1 to 10:1), which
4.5. (3R,4S,E)-6-(Dimethyl(phenyl)silyl)-4-methyl-1-
phenylhex-5-en-3-ol (6d)
A colorless oil: [
a
]
26.4 ꢁ4.61ꢂ (c 0.97, CHCl3); 89% yield; 93% ee;
D
1H NMR (400 MHz, CDCl3)
d 7.49e7.52 (m, 2H), 7.33e7.37 (m, 3H),
7.27e7.31 (m, 2H) 7.17e7.21 (m, 3H), 6.04 (dd, J¼18.8, 7.6 Hz, 1H),
5.90 (dd, J¼18.8, 0.8 Hz, 1H), 3.43e3.47 (m, 1H), 2.85 (ddd, J¼14.0,
10.0, 5.2 Hz, 1H), 2.68 (ddd, J¼13.6, 9.6, 6.8 Hz, 1H), 2.29e2.34 (m,
1H), 1.80e1.86 (m, 1H), 1.66e1.74 (m, 1H), 1.57 (d, J¼4.0 Hz, 1H), 1.05
(d, J¼6.8 Hz, 3H), 0.34 (s, 6H); 13C NMR (100 MHz, CDCl3)
d 150.3,
142.6, 139.1, 134.1, 130.7, 129.3, 128.8, 128.7, 128.1, 126.1, 74.2, 47.4,
36.4, 32.5, 16.3, ꢁ2.1; IR (neat) 3391, 3066, 3020, 2957, 2923, 1613,
1454, 1427, 1248, 1113, 1068, 1023, 998, 843, 827, 731, 698 cmCꢁ1
;
HRMS (ESI) m/z for C21H28OSiNa [MþNa]þ calcd 347.1807, found
347.1805.
4.6. (2S,3S,E)-1-(Benzyloxy)-5-(dimethyl(phenyl)silyl)-3-
methylpent-4-en-2-ol (6e)
26.7
A colorless oil: [
a
]
D
ꢁ16.1ꢂ (c 0.91, CHCl3); 75% yield; 96% ee;
1H NMR (400 MHz, CDCl3)
d 7.49e7.52 (m, 2H), 7.28e7.38 (m, 8H),
6.14 (dd, J¼18.8, 7.6 Hz, 1H), 5.85 (dd, J¼18.8, 1.2, Hz, 1H), 4.55 (s,
2H), 3.70e3.75 (m, 1H), 3.53 (dd, J¼9.6, 3.2 Hz, 1H), 3.42 (dd, J¼9.6,
7.6 Hz, 1H), 2.42e2.47 (m, 1H), 2.25 (d, J¼3.2 Hz, 1H), 1.06 (d,
J¼7.2 Hz, 3H), 0.34 (s, 6H); 13C NMR (100 MHz, CDCl3)
d 150.1, 139.3,
provided homoallylic alcohol 6a (57 mg, 85% yield) as a colorless
138.4, 134.1, 129.3, 129.2, 128.8, 128.09, 128.07, 73.8, 73.7, 72.8, 43.7,
16.2, ꢁ2.1, ꢁ2.2; IR (neat) 3401, 3068, 2959, 2929, 2873, 1722, 1614,
1454, 1428, 1372, 1316, 1248, 1114, 1028, 998, 842, 826, 733,
699 cmCꢁ1; HRMS (ESI) m/z for C21H28O2SiNa [MþNa]þ calcd
363.1756, found 363.1755.
26.8
oil. [
a
]
D
ꢁ83.8ꢂ (c 1.15, CHCl3); 85% yield; 95% ee; 1H NMR
(400 MHz, CDCl3)
d
7.27e7.49 (m, 10H), 6.12 (dd, J¼18.8, 7.6 Hz, 1H),
5.94 (d, J¼18.4 Hz, 1H), 4.42 (dd, J¼7.6, 3.6 Hz, 1H), 2.52e2.57 (m,
1H), 2.07 (d, J¼2.8 Hz, 1H), 0.90 (d, J¼6.8 Hz, 3H), 0.35 (s, 6H); 13C
NMR (100 MHz, CDCl3)
d 150.5, 142.7, 139.0, 134.1, 130.9, 129.3,
128.5, 128.1, 127.9, 127.1, 78.1, 49.2, 16.6, ꢁ2.14, ꢁ2.17; IR (neat)
3400, 3067, 2959, 2929, 1614, 1493, 1453, 1427, 1327, 1247, 1112,
1070, 1022, 998, 843, 822, 731, 699 cmCꢁ1; HRMS (ESI) m/z for
C19H24OSiNa [MþNa]þ calcd 319.1494, found 319.1500.
4.7. (3R,4S,E)-1-((tert-Butyldimethylsilyl)oxy)-6-(dimethyl(-
phenyl)silyl)-4-methyl-hex-5-en-3-ol (6f)
26.7
A colorless oil: [
a
]
D
ꢁ11.5ꢂ (c 1.35, CHCl3); 72% yield; 95% ee;
1H NMR (400 MHz, CDCl3)
d 7.50e7.53 (m, 2H), 7.33e7.36 (m, 3H),
4.3. (1E,3R,4S,5E)-6-(Dimethyl(phenyl)silyl)-4-methyl-1-
phenylhexa-1,5-dien-3-ol (6b)
6.14 (dd, J¼18.8, 7.2 Hz, 1H), 5.83 (dd, J¼18.8, 1.2 Hz, 1H), 3.86e3.91
(m, 1H), 3.78e3.84 (m, 1H), 3.72e3.76 (m, 3H), 3.08 (d, J¼2.0 Hz,
1H), 2.30e2.35 (m, 1H), 1.59e1.65 (m, 2H), 1.06 (d, J¼6.8 Hz, 3H),
0.91 (s, 9H), 0.33 (s, 6H), 0.08 (s, 6H); 13C NMR (100 MHz, CDCl3)
26.7
A colorless oil: [
a
]
D
ꢁ24.3ꢂ (c 1.41, CHCl3); 78% yield; 95% ee;
1H NMR (400 MHz, CDCl3)
d
7.52e7.50 (m, 2H), 7.23e7.38 (m, 7H),
d 150.9, 139.5, 134.1, 129.2, 128.8, 128.1, 75.1, 63.0, 46.8, 35.9, 26.2,
7.22e7.25 (m, 1H), 6.58 (d, J¼15.6 Hz, 1H), 6.19 (dd, J¼16.0, 7.2 Hz,
1H), 6.10 (dd, J¼18.8, 7.2 Hz, 1H), 5.95 (dd, J¼18.8, 0.8 Hz, 1H),
4.09e4.11 (m, 1H), 2.40e2.48 (m, 1H), 1.78 (d, J¼3.2 Hz, 1H), 1.07 (d,
18.5, 15.8, ꢁ2.05, ꢁ2.08, ꢁ5.1; IR (neat) 3436, 3069, 2956, 2930,
2858, 1614, 1471, 1463, 1428, 1253, 1088, 997, 837, 778, 731,
699 cmCꢁ1; HRMS (ESI) m/z for C21H38O2Si2Na [MþNa]þ calcd
401.2308, found 401.2301.
J¼6.8 Hz, 3H), 0.35 (s, 6H); 13C NMR (100 MHz, CDCl3)
d 150.2, 139.1,
137.1, 134.1, 131.9, 130.7, 130.5, 129.3, 128.9, 128.1, 128.0, 126.8, 76.4,
47.6, 16.1, ꢁ2.1; IR (neat) 3400, 3067, 2960, 1614, 1494, 1450, 1427,
4.8. (4S,5R,6S,7S,8S,Z)-7-((tert-Butyldimethylsilyl)oxy)-4-(di-
methyl(phenyl)silyl)-6,8-dimethyldeca-2,9-dien-5-ol (24c)
1317, 1247, 1113, 1069, 1023, 998, 967, 844, 829, 732, 695 cmCꢁ1
;
HRMS (ESI) m/z for C21H26OSiNa [MþNa]þ calcd 345.1651, found
345.1653.
Crystalline (dIpc)2BH (143 mg, 0.50 mmol) was weighed into
a round bottom flask containing a stir bar in a glove box (Note: The
crystalline borane should be crushed and pulverized to fine powder
with a glass rod in order to ensure efficient hydroboration). The
flask was capped with a rubber septum and removed from the
glove box. And then the flask was placed in a cold bath (ꢁ25 ꢂC).
Toluene (1 mL) was added slowly to the flask and the mixture
(suspension) was cooled to ꢁ25 ꢂC (w10 min). Racemic allenylsi-
lane (ꢀ)-4 (94 mg, 0.5 mmol) was added neat via a microliter
syringe. This mixture was stirred for 4 h at ꢁ25 ꢂC, and slowly
warmed to ꢁ15 ꢂC for 4 h, during, which time the solid (dIpc)2BH
4.4. (1R,2S,E)-1-Cyclohexyl-4-(dimethyl(phenyl)silyl)-2-
methylbut-3-en-1-ol (6c)
A colorless oil: [
a
]
26.6 ꢁ19.3ꢂ (c 1.86, CHCl3); 71% yield; 94% ee;
D
1H NMR (400 MHz, CDCl3)
d 7.49e7.52 (m, 2H), 7.33e7.36 (m, 3H),
6.08 (dd, J¼18.8, 7.6 Hz, 1H), 5.83 (d, J¼18.8 Hz, 1H), 3.11e3.16 (m,
1H), 2.39e2.48 (m, 1H), 1.72e1.83 (m, 3H), 1.60e1.69 (m, 2H), 1.42
(d, J¼4.4 Hz, 1H), 1.36e1.41 (m, 1H), 1.06e1.26 (m, 5H), 1.04 (d,
J¼6.8 Hz, 3H), 0.34 (s, 3H), 0.33 (s, 3H); 13C NMR (100 MHz, CDCl3)

M. Chen, W.R. Roush / Tetrahedron 69 (2013) 7551e7558
7557
dissolved to leave a colorless solution. The reaction mixture was
4.11. (3S,4R,6R,7R,E)-8-((tert-Butyldiphenylsilyl)oxy)-1-(dime-
thyl(phenyl)silyl)-6-methoxy-3,7-dimethyloct-1-en-4-ol (17)
cooled to ꢁ78 ꢂC and freshly prepared aldehyde 20c (51 mg,
0.2 mmol) was added at ꢁ78 ꢂC to the reaction mixture via mi-
croliter syringe. The mixture was stirred for 4 h at ꢁ78 ꢂC and
slowly warmed to ambient temperature and kept stirring for 8 h.
The reaction mixture was then cooled to 0 ꢂC with ice bath. To the
A colorless oil: [
a
]
27.1 ꢁ5.35ꢂ (c 1.35, CHCl3); 71% yield; 1H NMR
D
(400 MHz, CDCl3)
d
7.65e7.67 (m, 4H), 7.49e7.52 (m, 2H), 7.32e7.43
(m, 9H), 6.08 (dd, J¼18.8, 7.6 Hz, 1H), 5.85 (d, J¼18.8 Hz, 1H), 3.67
(dd, J¼10.0, 5.6 Hz, 1H), 3.54e3.64 (m, 2H), 3.52 (dd, J¼10.0, 6.4 Hz,
1H), 3.33 (s, 3H), 2.16e2.25 (m, 1H), 2.18 (d, J¼4.0 Hz, 1H), 1.89e1.95
(m, 1H), 1.55e1.61 (m, 1H), 1.45e1.52 (m, 1H), 1.06 (s, 9H), 1.00 (d,
J¼7.2 Hz, 3H), 0.95 (d, J¼6.8 Hz, 3H), 0.33 (s, 6H); 13C NMR
0
ꢂC mixture was added saturated NaHCO3 (0.5 mL) followed by
slow addition of 30% H2O2 (1.0 mL). The reaction was stirred vig-
orously for 5 h at room temperature. Brine (5 mL) was added, the
organic layer was separated and the aqueous layer was extracted
with Et2O (3ꢃ5 mL). The combined organic extracts were dried
over anhydrous magnesium sulfate, filtered, and concentrated un-
der reduced pressure. Purification of the crude product was per-
formed by flash column chromatography (gradient elution:
hexane:Et2O¼500:1 to 10:1), which provided alcohol 24c (62 mg,
(100 MHz, CDCl3)
d 150.6, 139.3, 136.0, 135.95, 134.2, 134.17, 134.12,
129.9, 129.2, 128.1, 128.0, 80.0, 72.1, 65.9, 58.6, 47.6, 39.2, 35.9, 27.2,
19.6, 16.5, 12.8, ꢁ2.08, ꢁ2.1; IR (neat) 3459, 3070, 2959, 2931, 2858,
1614, 1471, 1462, 1427, 1247, 1112, 998, 825, 737, 701 cmCꢁ1; HRMS
(ESI) m/z for C35H50O3Si2Na [MþNa]þ calcd 597.3196, found
597.3194.
70% yield) as a colorless oil. [
1H NMR (400 MHz, CDCl3)
a
]
27.1 ꢁ25.6ꢂ (c 1.78, CHCl3); 70% yield;
D
d
7.55e7.59 (m, 2H), 7.28e7.35 (m, 3H),
5.93 (ddd, J¼17.2, 10.0, 8.0 Hz, 1H), 5.56 (ddq, J¼11.2, 11.2, 1.6 Hz,
1H), 5.45 (dq, J¼11.2, 6.8 Hz, 1H), 4.88e4.94 (m, 2H), 3.86 (d,
J¼10.0 Hz, 1H), 3.68 (t, J¼3.2 Hz, 1H), 3.12 (br s, 1H), 2.33e2.41 (m,
1H), 2.14 (dd, J¼11.2, 2.0 Hz, 1H), 1.71e1.80 (m, 1H), 1.31 (dd, J¼6.8,
1.6 Hz, 3H), 0.98 (d, J¼7.2 Hz, 3H), 0.90 (s, 9H), 0.65 (d, J¼7.2 Hz, 3H),
0.35 (s, 3H), 0.31 (s, 3H), 0.04 (s, 3H), 0.03 (s, 3H); 13C NMR
4.12. (3R,4S,6R,7R,E)-8-((tert-Butyldiphenylsilyl)oxy)-1-(di-
methyl(phenyl)silyl)-6-methoxy-3,7-dimethyloct-1-en-4-ol
(18)
A colorless oil: [
NMR (400 MHz, CDCl3)
a]
27.2 8.25ꢂ (c 0.98, CHCl3); 63% yield; 8:1 dr; 1H
D
d
7.64e7.68 (m, 4H), 7.49e7.52 (m, 2H),
(100 MHz, CDCl3)
d 141.6, 139.5, 134.5, 129.0, 127.8, 126.6, 122.9,
7.31e7.44 (m, 9H), 6.10 (dd, J¼18.8, 7.2 Hz, 1H), 5.81 (dd, J¼18.8,
0.8 Hz, 1H), 3.70 (dd, J¼10.0, 6.0 Hz, 1H), 3.60e3.65 (m, 1H),
3.51e3.56 (m, 2H), 3.30 (s, 3H), 3.21 (d, J¼1.6 Hz, 1H), 2.27e2.34 (m,
1H), 1.95 (ddd, J¼13.2, 6.8, 3.6 Hz, 1H), 1.43e1.52 (m, 2H), 1.06 (s,
9H),1.04 (d, J¼6.8 Hz, 3H), 0.88 (d, J¼6.8 Hz, 3H), 0.321 (s, 3H), 0.317
114.6, 80.6, 73.4, 42.3, 40.9, 33.0, 26.3, 20.3, 18.0, 13.5, 13.3, ꢁ3.1,
ꢁ3.4, ꢁ3.9, ꢁ4.1; IR (neat) 3500, 3070, 2957, 2930, 2859, 1641, 1471,
1463, 1427, 1372, 1252, 1113, 1024, 837, 733, 700 cmCꢁ1; HRMS (ESI)
m/z for C26H46O2Si2Na [MþNa]þ calcd 469.2934, found 469.2941.
(s, 3H); 13C NMR (100 MHz, CDCl3)
d 150.8, 139.5, 136.0, 135.94,
4.9. (4S,5R,6S,7R,8R,Z)-9-((tert-Butyldiphenylsilyl)oxy)-4-(di-
methyl(phenyl)silyl)-7-methoxy-6,8-dimethylnon-2-en-5-ol
(24a)
134.2, 134.13, 130.0, 129.2, 128.8, 128.1, 128.0, 83.4, 75.1, 65.4, 57.8,
46.9, 38.4, 34.5, 27.3, 19.6, 15.5, 12.4, ꢁ2.04, ꢁ2.09; IR (neat) 3435,
3070, 2959, 2930, 2858, 1462, 1427, 1247, 1112, 1082, 824, 737,
700 cmCꢁ1; HRMS (ESI) m/z for C35H50O3Si2Na [MþNa]þ calcd
597.3196, found 597.3214.
A colorless oil: [
(400 MHz, CDCl3)
a
]
27.2 ꢁ15.8ꢂ (c 1.82, CHCl3); 62% yield; 1H NMR
D
d
7.58e7.71 (m, 6H), 7.31e7.44 (m, 9H), 5.61 (ddq,
J¼11.2, 11.2, 1.6 Hz, 1H), 5.45 (dq, J¼11.2, 6.8 Hz, 1H), 3.98 (t,
J¼1.6 Hz, 1H), 3.70 (dd, J¼10.0, 5.6 Hz, 1H), 3.60 (d, J¼9.2 Hz, 1H),
3.52 (dd, J¼10.0, 2.4 Hz,1H), 3.34 (s, 3H), 3.00 (dd, J¼7.2, 4.0 Hz,1H),
2.20 (bd, J¼11.2 Hz, 1H), 1.91e1.97 (m, 1H), 1.76e1.82 (m, 1H), 1.31
(dd, J¼6.8, 1.6 Hz, 3H), 1.04 (s, 9H), 0.96 (d, J¼6.8 Hz, 3H), 0.62 (d,
J¼6.8 Hz, 3H), 0.38 (s, 3H), 0.32 (s, 3H); 13C NMR (100 MHz, CDCl3)
Acknowledgements
Financial support provided by the National Institutes of Health
(GM038436) is gratefully acknowledged. We thank Eli Lilly for
a predoctoral fellowship to M.C.
d
139.7, 136.0, 135.95, 134.5, 134.3, 134.2, 129.9, 128.9, 127.9,
127.7, 126.9, 122.6, 91.4, 75.5, 65.5, 61.1, 40.1, 40.0, 32.7, 27.3, 19.6,
15.7, 15.4, 13.4, ꢁ3.1, ꢁ3.2; IR (neat) 3470, 3070, 2960, 2931, 2858,
1471, 1427, 1391, 1244, 1112, 1072, 840, 821, 737, 701 cmCꢁ1; HRMS
(ESI) m/z for C36H52O3Si2Na [MþNa]þ calcd 611.3353, found
611.3361.
References and notes
1. (a) Roush, W. R. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon:
Oxford, UK, 1991; Vol. 2, p 1; (b) Yamamoto, Y.; Asao, N. Chem. Rev. 1993, 93,
2207; (c) Denmark, S. E.; Almstead, N. G. In Modern Carbonyl Chemistry; Otera, J.,
Ed.; Wiley-VCH: Weinheim, Germany, 2000; p 299; (d) Chemler, S. R.; Roush,
W. R. In Modern Carbonyl Chemistry; Otera, J., Ed.; Wiley-VCH: Weinheim,
Germany, 2000; p 403; (e) Denmark, S. E.; Fu, J. Chem. Rev. 2003, 103, 2763; (f)
ꢁ
ꢁ
4.10. (4S,5R,6S,7R,8S,Z)-9-((tert-Butyldiphenylsilyl)oxy)-4-(di-
methyl(phenyl)silyl)-7-methoxy-6,8-dimethylnon-2-en-5-ol
(24b)
Lachance, H.; Hall, D. G. Org. React. 2008, 73, 1; (g) Yus, M.; Gonzales-Gomez, J.
C.; Foubelo, F. Chem. Rev. 2011, 111, 7774.
2. (a) Pietruszka, J.; Schone, N. Angew. Chem., Int. Ed. 2003, 42, 5638; (b) Pelz, N. F.;
Woodward, A. R.; Burks, H. E.; Sieber, J. D.; Morken, J. P. J. Am. Chem. Soc. 2004,
126, 16328; (c) Sieber, J. D.; Morken, J. P. J. Am. Chem. Soc. 2006, 128, 74; (d) Ito,
H.; Ito, S.; Sasaki, Y.; Matsuura, K.; Sawamura, M. J. Am. Chem. Soc. 2007, 129,
14856; (e) Peng, F.; Hall, D. G. J. Am. Chem. Soc. 2007, 129, 3070; (f) Chen, M.;
Roush, W. R. Org. Lett. 2010, 12, 2706; (g) Althaus, M.; Mahmood, A.; Suarez, J.
R.; Thomas, S. P.; Aggarwal, V. K. J. Am. Chem. Soc. 2010, 132, 4025; (h) Kliman,
L. T.; Mlynarski, S. N.; Ferris, G. E.; Morken, J. P. Angew. Chem., Int. Ed. 2012, 51,
521; (i) Ferris, G. E.; Hong, K.; Roundtree, I. A.; Morken, J. P. J. Am. Chem. Soc.
2013, 135, 2501.
3. For a recently review on allenes in asymmetric synthesis: Yu, S.; Ma, S. Angew.
Chem., Int. Ed. 2012, 51, 3074.
4. (a) Chen, M.; Roush, W. R. J. Am. Chem. Soc. 2011, 133, 5744; (b) Chen, M.; Ess, D.
H.; Roush, W. R. J. Am. Chem. Soc. 2010, 132, 7881; (c) Han, J.-L.; Chen, M.; Roush,
W. R. Org. Lett. 2012, 14, 3028.
A colorless oil: [
(400 MHz, CDCl3)
a
]
26.9 ꢁ1.58ꢂ (c 3.16, CHCl3); 67% yield; 1H NMR
D
d
7.60e7.67 (m, 6H), 7.31e7.45 (m, 9H), 5.69 (ddq,
J¼11.2, 11.2, 1.6 Hz, 1H), 5.44 (dq, J¼10.8, 6.8 Hz, 1H), 4.32 (dd, J¼2.4,
1.2 Hz, 1H), 3.68 (bd, J¼8.4 Hz, 1H), 3.47e3.56 (m, 2H), 3.384 (s, 3H),
3.38 (dd, J¼8.8, 1.6 Hz, 1H), 2.22 (dt, J¼11.6, 2.0 Hz, 1H), 1.80e1.85
(m, 1H), 1.69e1.75 (m, 1H), 1.31 (dd, J¼6.8, 1.6 Hz, 3H), 1.05 (s, 9H),
0.72 (d, J¼6.8 Hz, 3H), 0.62 (d, J¼6.4 Hz, 3H), 0.40 (s, 3H), 0.34 (s,
3H); 13C NMR (100 MHz, CDCl3)
d 139.7, 135.91, 135.89, 134.6, 134.1,
134.0, 130.0, 128.9, 128.01, 128.0, 127.7, 127.0, 122.5, 87.5, 75.4, 66.7,
61.3, 40.4, 39.0, 32.9, 27.2, 19.6, 14.6, 13.4, 10.2, ꢁ3.2; IR (neat) 3468,
3070, 3016, 2960, 2931, 2858, 1471, 1428, 1392, 1245, 1112, 1071,
823, 738, 701 cmCꢁ1; HRMS (ESI) m/z for C36H52O3Si2Na [MþNa]þ
calcd 611.3353, found 611.3358.
5. (a) Sun, H.; Abbott, J. R.; Roush, W. R. Org. Lett. 2011, 13, 2734; (b) Yin, M.; Roush,
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426; (d) Chen, M.; Roush, W. R. Org. Lett. 2012, 14, 1556; (e) Chen, M.; Roush, W.
R. Org. Lett. 2012, 14, 1880; (f) Chen, M.; Roush, W. R. J. Org. Chem. 2013, 78, 3.
6. Chen, M.; Roush, W. R. Org. Lett. 2013, 15, 1662.

7558
M. Chen, W.R. Roush / Tetrahedron 69 (2013) 7551e7558
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Kusumi, T.; Kashman, Y.; Kakisawa, H. J. Am. Chem. Soc. 1991, 113, 4092.
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